Films from aqueous dispersions of block copolymers having hydrogenated conjugated diene block

ABSTRACT

Aqueous dispersions, and films prepared therefrom, comprising an organic phase of block copolymers and optional extenders wherein the block copolymers corresponds to the formula: 
     
         A-B-X.sub.m -(B-A).sub.n 
    
     wherein each A is a polymer block of a monovinylidene aromatic monomer and conjugated dienes, each B is a polymer block of one or more conjugated dienes and, optionally, one or more monovinylidene aromatic monomers, X is the remnant of a multifunctional coupling agent, m is 0 or 1, and n is an integer from 1 to 5. Each A polymer block has a weight average molecular weight from 4,000 to 15,000 Daltons. Each B polymer block has a weight average molecular weight from 20,000 to 200,000 Daltons. The total monovinylidene monomer content is from 6 to 30 percent by weight of the organic phase. The effective phase volume of the A polymer block in the organic phase is from 8 to 20 percent. Thin elastomeric articles prepared from the emulsions have improved tensile strength properties. Also claimed is a process for the preparation of such films.

BACKGROUND OF THE INVENTION

The present invention relates to high-strength films prepared fromaqueous dispersions of block copolymers of vinyl aromatic monomers andconjugated dienes wherein the conjugated diene block is hydrogenated.

Block copolymers of the conventional A-B-A type form strong films whencast from solutions in organic solvents. The use of aqueous dispersionsor latices to form films or articles of intricate design is preferred tothe use of casting from solutions because no objectionable fumes arereleased during the drying step. However, films of comparable thicknessprepared by casting from their aqueous dispersions or latices aregenerally weak.

To improve the strength of such films, U.S. Pat. No. 3,360,599 taughtthe use of an annealing procedure. Disadvantageously, this annealingprocedure requires elevated temperatures and/or long annealing times. Asa consequence, the resulting films often have inferior strengthproperties, due to polymer degradation, and/or the time required forfilm formation is unacceptably long.

U.S. Pat. No. 4,199,490 teaches the addition of a second aqueousdispersion comprising a rubber, synthetic resin or a mixture thereof toenable the formation of films upon drying at room temperature. In theabsence of such additive, the block copolymer dispersion did not possessadequate film-forming properties at moderate or low temperatures.

In U.S. Pat. No. 3,238,173, there was disclosed the preparation ofconcentrated aqueous dispersions by contacting the dilute latex with analiphatic hydrocarbon that is a non-solvent for the non-elastomericblock, removing the hydrocarbon and concentrating the latex. The use ofsuch non-solvents is undesirable, due to the added complexity of theprocess and the presence of residual organic contaminants in theresulting films.

Many block copolymers contain residual unsaturation in the conjugateddiene block. Polymers containing residual unsaturation are susceptibleto degradation due to exposure to ultraviolet light and/or ozone. Insome applications, such degradation is unacceptable.

Accordingly, there remains a need to provide films prepared from aqueousdispersions of block copolymers having improved strength properties. Inaddition, it would be desirable to provide a process capable ofpreparing strong films from aqueous latices of block copolymers thatuses relatively short times and mild temperature conditions for theannealing step to thereby avoid significant polymer degradation. Itwould be desirable to provide a process for the preparation of thinelastomeric articles by film deposition from a block copolymer latexthat avoids the use or reduces the amount of additives. It is desirableto prepare films which have good stability in the presence of heat,ultraviolet light and ozone.

SUMMARY OF THE INVENTION

Accordingly, the present invention relates to a stable aqueousdispersion which is capable of forming a coherent, elastomeric, solidfilm which, after drying and annealing at 90° C. for 30 minutes,demonstrates a tensile strength of about 11.0 MPa or greater, whereinthe dispersion comprises:

I. an organic phase comprising

(a) one or more block copolymer(s) corresponding to the formula

    A-B-X.sub.m -(B-A).sub.n                                   (I)

wherein each A is a polymer block derived from monomers comprising oneor more monovinylidene aromatic monomers, each B is a polymer blockderived from monomers comprising one or more conjugated dienes and,optionally, one or more monovinylidene aromatic monomers, X is theremnant of a multifunctional coupling agent, m is 0 or 1, and n is aninteger from about 1 to about 5, each A polymer block has a weightaverage molecular weight from about 4,000 to about 15,000 Daltons, eachB polymer block has a weight average molecular weight from about 20,000to about 200,000 Daltons, wherein the block copolymer is hydrogenatedsuch that about 99 mole percent or greater of the residual olefinicunsaturation derived from the conjugated dienes is eliminated andcontains sufficient branching such that the block copolymer iselastomeric;

(b) optionally, an extender for the block copolymer which is compatiblewith the B polymer block; and

wherein the organic phase contains from about 6 to about 30 percent byweight of units derived from monovinylidene aromatic monomers, and theeffective phase volume of the A polymer block in the organic phase isfrom about 8 to about 20 volume percent; and

II. a surfactant in a sufficient amount to emulsify the organic phase inwater.

In another embodiment, the invention comprises a high-strength filmcomprising the organic phase, described hereinbefore, wherein the filmexhibits a tensile strength at break of about 11.0 MPa or greater afterannealing at 90° C. for 30 minutes.

In yet another embodiment, the invention comprises a process forpreparing a film which comprises (1) depositing an aqueous dispersion ofthe invention on a surface under conditions so as to form a film, (2)removing the film from the surface and (3) annealing the film underconditions such that the annealed film exhibits tensile strength atbreak of about 11.0 MPa or greater.

Surprisingly, such block copolymers readily form thin films bydeposition onto solid surfaces from an aqueous dispersion. Such filmsmay be dried to form coherent, elastomeric, solid film articles havinghigh annealed strength properties using short annealing times and mildannealing temperatures. Examples of such articles include surgicalgloves, examination gloves, condoms, catheters, balloons and other thinelastomeric articles. If a tackifier and, optionally, other formulantsknown to one skilled in the art are combined with the block copolymer,films having adhesive properties may also be prepared. Such films may bedeposited onto a thin, flexible substrate for use as pressure sensitivetapes, packaging tapes, masking tapes and labels. Such films andarticles also exhibit excellent environmental and ozone stability.

DETAILED DESCRIPTION OF THE INVENTION

It has been discovered that by careful selection of the block copolymerand the total volume of the monovinylidene aromatic polymer block (Apolymer block), stable aqueous emulsions can be prepared which formstrong films. In selecting appropriate block copolymers, the weightaverage molecular weight of the monovinylidene aromatic monomer block (Apolymer block) must be within the limits defined herein. If the Apolymer block chain length is too high, the annealing time required toform a high-strength film becomes unacceptably long. If the A polymerblock chain length is too low, the films prepared do not exhibitacceptable tensile strengths. Preferably, the A polymer block has aweight average molecular weight from about 4,000 to about 15,000 Daltonsand more preferably of from about 6,500 to about 15,000 Daltons and theB polymer block has a weight average molecular weight from about 50,000to about 120,000 Daltons. In the embodiment where the block copolymer isin radial form, the diene blocks' weight average molecular weight canrange from about 50,000 to about 240,000 Daltons. The total volume ofthe A polymer block phase in the organic phase is important, in that, ifthe volume of the A polymer block is too high, stable emulsions cannotbe formed using a relatively low amount of surfactants. If the A polymerblock phase volume in the organic phase is too low, the films preparedfrom the block copolymers will not exhibit the required tensilestrengths. Preferably, the amount volume of A polymer block in theorganic phase is from about 8 percent to about 20 percent by volume.Most preferably, the A polymer block has an effective phase volume fromabout 10 to about 18 percent of the organic phase.

The A polymer block comprises one or more monovinylidene aromaticmonomers. The A polymer block may comprise no more than about 1 percentby weight of an ethylenically unsaturated comonomer which polymerizesunder anionic conditions. Preferably the A polymer block contains nocomonomers. Preferable monovinylidene aromatic monomers for use hereininclude styrene and alkyl substituted derivatives of styrene. Examplesinclude styrene, α-methylstyrene, and vinyl toluene. A more preferredmonoaromatic monomer is styrene.

The B polymer block comprises 1 or more conjugated dienes and optionallymonovinylidene aromatic monomers. Preferably the B block furthercomprise no more than about 1 percent by weight of an ethylenicallyunsaturated co-monomer which is copolymerizable under anionicconditions, other than a monovinylidene aromatic monomer. Preferably,the ethylenically unsaturated co-monomer useful in this inventionconsists of carbon and hydrogen. Conjugated dienes preferably employedin the present invention include 1,3-butadiene, isoprene or mixturesthereof. Preferably, the conjugated diene is butadiene.

Both linear and radial block copolymers are suitably employed in theinvention. Most preferably, however, the block copolymers are triblockcopolymers, that is, n in Formula (I) is equal to 1.

The block copolymers may be partially tapered, fully tapered oruntapered polymers. By the term "tapered" is meant that the B blockchanges gradually from diene rich or pure diene homopolymer in thecenter to include increasing proportions of monovinylidene aromaticmonomer in a gradual conversion towards the junction of the A polymerblock (the monovinylidene aromatic polymer block) of the block copolymerand terminates in pure homopolymer of the monovinylidene aromaticmonomer. Preferably the B block contains no more than 20 weight percentmonovinylidene aromatic monomers and more preferably no more than 10weight percent monovinylidene aromatic monomers. The conversion may besymmetrical or unsymmetrical with respect to the center of the B polymerblock. Triblock copolymers possessing taperness at only one junction arereferred to as "half-tapered" polymers.

The block copolymers used in this invention are hydrogenated toeliminate the olefinic unsaturation in the diene blocks. Preferably, asignificant portion of the olefinic unsaturation is eliminated byhydrogenation while a significant portion of the aromatic unsaturationderived from the monovinylidene aromatic monomers is retained. Morepreferably, about 99 mole percent or greater of the olefinicunsaturation is eliminated by hydrogenation. More preferably, about 90mole percent or greater of the aromatic unsaturation is retained. Evenmore preferably, about 95 mole percent or greater of the aromaticunsaturation is retained, and most preferably, about 99 mole percent orgreater of the aromatic unsaturation is retained.

The block copolymers must have sufficient branching in the diene blockto prevent formation of crystalline domains to retain the elastomericproperties of the block copolymer. As used herein, "branching" meansafter polymerization, lower alkyl substituents are pendant from theportion of the block copolymer derived from dienes. For example, ifisoprene is used to prepare the desired diene block, methyl groups arependant from the chain. Where a straight-chain conjugated diene, such asbutadiene, is used, there must be a sufficient amount of 1,2-addition toprevent formation of crystalline domains. 1,2-Addition results when thepolymerization occurs through one olefinic bond rather than through botholefinic bonds. When polymerization occurs through one olefinic bond, anunsaturated group is pendant from the polymer chain. Where astraight-chain conjugated diene is used, the 1,2-addition is preferablyabout 25 mole percent or greater, more preferably about 30 mole percentor greater and most preferably about 35 mole percent or greater. If toomuch branching is present, the resultant polymer is no longerelastomeric. Preferably, the 1,2-addition is about 60 percent or lessand more preferably about 50 percent or less. The amount of 1,2-additionfor butadiene can be increased by the use of a polar solvent in thepolymerization. Preferably, only a portion of the solvent used is polar.A preferable solvent for this purpose is tetrahydrofuran. "Derived frommonomers," as used herein, means that the polymer block(s) referred tocomprise the residue of the monomers referred to in the polymer block.Residue refers to the portion of the monomer which remains in thepolymer block after polymerization. "Organic phase," as used herein,refers to all of the hydrocarbon based materials in the emulsion, exceptthe surfactant. Such materials include the block copolymers and anyoptional extender.

A blend of two or more block copolymers may be used in this invention.All of the block copolymers used preferably have A polymer blocks whichhave weight average molecular weights in the range of from about 4,000to about 15,000 Daltons. The composition weighted average units derivedfrom monovinylidene aromatic monomers content of the blended copolymersis preferably from about 6 to about 30 percent by weight. One or more ofthe components may have A polymer blocks derived from monovinylidenearomatic monomers content outside of the stated range, provided theaverage is within the stated range.

In the embodiment wherein one of the block copolymers in such a blendcontains units derived from monovinylidene aromatic monomers at a levelabove 30 weight percent, it is preferred that such content be about 40weight percent or less and, more preferably, about 35 weight percent orless. Preferably, the total amount of block copolymer, having an Apolymer block content above about 30 percent by weight, is about 35percent by weight or less and, more preferably, about 30 percent byweight or less.

The block copolymers can be blended in bulk and thereafter emulsified.Optionally, the block copolymers may be emulsified separately and theemulsions can be blended. Methods of blending the bulk block copolymersor aqueous emulsions of the block copolymers are well known in the art.

In some embodiments of the invention, the one or more block copolymersmay have an effective phase volume of the A polymer block in the organicphase which is greater than desired. In order to reduce the phase volumeof the A polymer block in the organic phase, an extender may be blendedwith the block copolymer.

Extenders useful in the invention are non-volatile organic materialswhich are compatible with the B polymer block, that is, such extendersare soluble in the B polymer block or form a single phase with the Bpolymer block. Further, useful extenders do not degrade the propertiesof the films prepared from the aqueous emulsions of the invention suchthat the tensile strengths are less than 11.0 MPa after the films areannealed at 90° C. for 30 minutes.

Among preferred extenders are hydrocarbon oils, polymers or oligomersderived from monomers having olefinic unsaturation compatible with the Bpolymer block, or mixtures thereof. More preferred extenders are thealiphatic hydrocarbon and naphthenic oils with the most preferred classof extenders being the aliphatic hydrocarbon oils. The preferredaliphatic hydrocarbon and naphthenic oils are selected according to theultimate end-use and the cost of such oils. Among preferred oils areTufflo™ 6056 mineral oil (trademark of Atlantic Richfield Company) andShellflex™ 371 mineral oil (trademark of Shell Oil Company).

The preferred polymers useful as extenders includestyrene-ethylene-butene diblock, polyethylene vinyl acetate copolymers,ethylene and methacrylate copolymers, ethylene-propylene diene monomerbased polymers, and ethylene-styrene copolymers. Other preferredpolymers include polyisoprene, polybutadiene, styrene-butadiene randomcopolymers and hydrogenated forms of such polymers. Most preferredpolymers include polyisoprene, polybutadiene and the hydrogenated formsof such polymers.

The extenders are present in a sufficient amount to achieve the desiredeffective phase volume of the A polymer block. If too much extender isused, the films prepared from the aqueous emulsions would not meet thetensile strength requirements. The amount of extender is preferablyabout 45 percent by weight or less of the organic phase, morepreferably, about 40 percent by weight or less and, even morepreferably, about 35 percent by weight or less. If present, the extenderis preferably present in an amount of about 5 percent by weight orgreater of the organic phase and, preferably, 10 percent by weight orgreater.

The extender can be blended with the block copolymer in bulk and theblend can be emulsified. Alternatively, the extender and blockcopolymers can be separately emulsified and the emulsions can be blendedto achieve the desired organic phase composition. In yet anotherembodiment, the extender may be added directly to an emulsion of theblock copolymers. Methods of performing such blending are well known inthe art.

To achieve the required organic phase composition, a blend of two ormore copolymers and one or more extenders may be used in combination.

Effective phase volume or volume percent of the A polymer blocks in theorganic phase may be less than the weight percent of units derived frommonovinylidene aromatic monomers in such copolymers. Especially if oneor more of the polymers is tapered, the A polymer blocks are morecompatible and, therefore, more soluble in the phase containing the Bpolymer block of the resulting multiple phase structure compared to puremonovinylidene aromatic homopolymer blocks. Due to such solubility, thevolume of the phase segregated A polymer block is less than the contentof the units derived from monovinylidene aromatic monomer expressed byweight. Accordingly, the percentage of the A polymer blocks in theorganic phase, measured as a volume percent, is less than the percentageof units of monovinylidene aromatic monomer as measured by weight.

In order to determine the volume percent of the A polymer block, thecorresponding weight percentage of units derived from monovinylidenearomatic monomer is divided by a correction factor. The correctionfactor is a value equal to the sum of ratios of each monomer's contentin weight percent divided by the respective density of a homopolymer ofsuch monomer. For a two-component block copolymer, this may be expressedas follows:

    %(vol.sub.a)=%(wt.sub.a)/D.sub.a /(%(wt.sub.a)/D.sub.a +%(wt.sub.b)/D.sub.b)(II)

where:

%(vol_(a)) is the effective phase volume in percent for themonovinylidene aromatic polymer block;

%(wt_(a)) and %(wt_(b)) are the respective weight percent contents ofmonovinylidene aromatic monomer and hydrogenated diene monomer in theblock copolymer; and

D_(a) and D_(b) are the respective densities of homopolymers, themonovinylidene aromatic monomer and hydrogenated diene monomer.

In those embodiments where an extender is present, the effective phasevolume of the A polymer block in the organic phase is represented byFormula III:

    %(vol.sub.a)=%(wt.sub.a)/D.sub.a /(%(wt.sub.a)/D.sub.a +%(wt.sub.b)/D.sub.b +%(wt.sub.e)/D.sub.e)                                     (III)

where:

%(wt_(e)) is the weight percent extender present, and

D_(e) is the density of the extender present.

For tapered block copolymers, the above numerator is further multipliedby a correction factor equal to 1-τ (where τ is the degree of taperness)to account for the isolated monovinylidene aromatic polymer content. Thedegree of taperness in the block copolymer is the percentage of totalmonovinylidene aromatic polymer units that are isolated. Such isolatedmonovinylidene aromatic polymer units are those segments ofmonovinylidene aromatic polymer surrounded on both sides by conjugateddiene polymer units and are easily determined by the use of nuclearmagnetic resonance spectroscopy as disclosed in Mochel, Rubber Chemistryand Technology, Vol. 40, p. 1200 (1967). Because such isolated polymerunits do not contribute significantly to the phase represented by thepolymer block A (monovinylidene aromatic polymer block), tapered blockcopolymers can possess an effective monovinylidene aromatic polymerphase volume that is significantly less than the weight percentmonovinylidene aromatic monomer content.

At lower monovinylidene aromatic polymer block effective phase volumes,especially for polymers wherein the monovinylidene aromatic polymerblock molecular weight is relatively low, the tensile properties of theresulting films are unacceptably low. At higher monovinylidene aromaticpolymer block effective phase volumes, the dispersion does not readilyform films, especially at mild temperatures from 25° C. to 90° C.Moreover, films from such polymers require longer periods of time underannealing conditions and/or higher annealing temperatures to achievemaximum tensile strength properties. Such films are subject to polymerdegradation resulting in films possessing poor tensile properties,especially ultimate tensile strength.

Preferably, the weight average molecular weight (M_(w)) of the blockcopolymers is about 45,000 Daltons or greater to 240,000 Daltons, morepreferably, about 50,000 or greater, most preferably, about 55,000 orgreater. Preferably, the weight average molecular weight of the blockcopolymers is about 430,000 or less, more preferably 300,000 Daltons orless, even more preferably 240,000 Daltons or less, even more preferablyabout 200,000 or less and most preferably 180,000 Daltons or less. Inthe embodiment where the block copolymer is a radial block copolymer,the weight average molecular weight is preferably about 300,000 or less.In measuring the molecular weights of copolymers herein, the techniqueemployed is that of gel permeation chromatography (GPC) usingpolystyrene standards. The molecular weights for the styrene blocks arebased on the polystyrene standards. The molecular weights for all otherblocks are based on the polystyrene standards and corrected according toRunyon et al. vs. Applied Polymer Science, 13, p. 2359 et. seq. 1969,and L. H. Tung, J. Applied Polymer Science 24, 953 (1979) bothincorporated herein by reference.

It is believed (without agreeing to be bound by such belief) that whenthe monovinylidene aromatic polymer blocks possess the previously statedeffective phase volume, the monovinylidene aromatic polymer blockscoalesce, thereby causing the polymer matrix to possess a particulatedor spherical morphology instead of a cylindrical or lamellar morphology.Such morphology is desirable for the formation of films from latexeshaving good strength properties and film formation rates. Suchmorphology as well as the concept of polymer block phase volume, aredisclosed in S. L. Aggarwal, Block Polymers, Plenum Press, pp. 102-103,(1970). It is further believed (without agreeing to be bound by suchbelief) that the particulated or spherical morphology which is presentin the A polymer block is the discontinuous phase which facilitates theformation of stable emulsions and strong films.

Block copolymers and techniques for their preparation are well known inthe art. Such polymers may be prepared by sequential anionicpolymerization utilizing alkyllithium initiators, such asn-butyl-lithium and sec-butyllithium. They may also be prepared bycoupling of living block copolymers or by using soluble difunctionallithium initiators such as1,3-phenylene-bis(3-methyl-1-phenylpentylidene)-bis-(lithium), orsimilar initiator as disclosed in U.S. Pat. No. 4,196,154 (incorporatedherein by reference). The block copolymers may be tapered or untapered.That is, the junction between the separate blocks may be gradual orabrupt. Untapered block copolymers may be formed by completelypolymerizing each monomer component before adding the next block-formingmonomer to the reaction medium containing the living polymer anion.Tapered block copolymers may be formed by copolymerizing a mixture ofthe monomers using the previously mentioned difunctional initiators. Dueto the differing reactivities of the monomers, a relatively pure dieneblock initially forms, followed by an intermediate portion of suchpolymer containing increasing amounts of interspersed monovinylidenearomatic polymer and, finally, a relatively pure monovinylidene aromaticpolymer block.

After polymerization according to one of the foregoing anionicpolymerization techniques, the living polymer anion is terminated byaddition of a terminating agent containing a reactive hydrogen, orcoupled by a coupling agent containing multiple leaving groups.Preferable terminating agents include water, alcohols and carboxylicacids. Preferable coupling agents include ethylene dibromide, methylenechloride, carbon tetrachloride, silicon tetrachloride anddichlorodimethylsilane. Additional additives can be added to thereaction mixture before or after the polymerization is completed forpurposes of stabilizing the polymer, preventing discoloration or for anyother suitable purpose. The polymerization is normally conducted in anorganic solvent such as hexane, toluene, cyclohexane, benzene or amixture thereof.

The block copolymers can be hydrogenated by conventional methods ofhydrogenation. The hydrogenation is preferably carried out usingmolecular hydrogen and a catalyst based on metals or metal salts ofGroup VIII of the Periodic Table. It may be affected in theheterogeneous phase, for example, using Raney nickel, or in thehomogeneous phase using a catalyst based on salts, in particularcarboxylates, alkoxides or enolates of cobalt, nickel or iron, which arecombined with metal alkylates, in particular aluminum alkylates. Otheruseful catalysts include organo metallic titanium compounds, see U.S.Pat. Nos. 3,920,745, 4,980,421 and 4,673,714, incorporated herein byreference; among such catalysts are bis(cyclopentadienyl)titaniumcompounds, see U.S. Pat. Nos. 5,141,997 and 5,039,755, incorporatedherein by reference. Processes for the selective hydrogenation of blockcopolymers are described in U.S. Pat. Nos. 4,595,749; 3,595,942;3,113,986 and 4,226,952, incorporated herein by reference.

To isolate the hydrogenated polymer, the polymerization mixture can beheated directly to dryness or, alternatively, treated with steam withthe solvent being distilled off. It can also be precipitated in anexcess of a non-solvent, for example, ethanol, and isolated mechanicallyand dried or worked up by devolatilization in an extruder.

The hydrogenation may be conducted at temperatures from about 5° C. toabout 200° C. and at pressures from 0.1 atm to 80 atm. Preferredtemperatures are from about 40° C. to about 140° C. and preferredpressures are from about 0.5 atm to about 20 atm. Contact times willrange from about 0.01 hour to about 10 hours in the treating steps andfrom about 0.01 to about 14 hours in the phase separation step, butpreferred contact times are about 0.02 hour to about 1 hour in thetreating step and about 0.02 to about 1 hour in the phase separationstep.

Surfactants useful in the invention are those which emulsify the blockcopolymer(s) and optional diluent in water. Anionic, cationic andnonionic surfactants may be used, with the anionic and cationicsurfactants being preferred. Even more preferred surfactants are theC₁₂₋₃₀ saturated and unsaturated carboxylic acids or salts thereof,sulfated alkylphenoxypoly(ethyleneoxy)ethanol, alkali or ammonium saltsand dialkyl esters of alkali metal sulfosuccinic acid (for exampleAerosol™ OT dioctyl ester of sodium sulfosuccinic acid, available fromAmerican Cyanamid). Even more preferred are the C₁₂₋₃₀ saturated andunsaturated carboxylic acids or salts thereof. Preferred counterions arethe alkali metals and ammonium ions and more preferred are potassiumions. Among the most preferred surfactants are stearic acid, linoleicacid, linolenic acid, lauric acid, oleic acid (for example, Industrene™105 oleic acid, available from Humko Chemical), alkali metal salts ofdisproportionated rosin (for example, Dresenate™ 214 potassium salt ofdisproportionated rosin, predominantly abietic acid). Preferably, thesurfactants have a hydrophilic-lipophilic-balance (HLB) of about 15 orgreater and, more preferably, an HLB of about 18 or greater. HLB isdescribed in and can be determined according to Becker Emulsions: Theoryand Practice, pp. 232-251, Krieger Publishing Co., Huntington, N.Y.(1977 ).

The surfactant is present in a sufficient amount to emulsify the blockcopolymer(s) and optional diluent. If too much surfactant is used toprepare the aqueous emulsions, films prepared from the aqueous emulsionswill not demonstrate the desired tensile properties. The reason is thata significant amount of the surfactant may remain in the film which isformed from the aqueous emulsion. The maximum amount of surfactantuseful is related to how much surfactant is retained in the film. Morethan this amount may be used if the excess portion is removed prior tofilm formation or can be leached from the film prior to annealing.Preferably, about 0.5 percent by weight or more of surfactant, based onthe organic phase, is present and, more preferably, 1 percent by weightor more is present and, even more preferably, about 2 percent by weightor more is present. Preferably, about 10 percent by weight or less ofsurfactant, based on the organic phase, is used, more preferably, about8 percent by weight is used and, even more preferably, about 6 percentby weight or less is used. Where a portion of the surfactant is removedprior to film formation, up to about 20 percent by weight may be used,provided no more than about 10 percent by weight is present in the finalfilm.

To produce an aqueous dispersion, the polymer, usually in the form of asolution in an organic solvent, is dispersed in water using a suitablesurfactant and the organic solvent is removed. One suitable procedure ispreviously disclosed in U.S. Pat. No. 3,238,173 incorporated herein byreference. Emulsification can take place by any of the well-known meansfor this purpose and the specific means utilized does not form anessential aspect of the present invention.

In one embodiment, block copolymer and optional diluent dissolved inorganic solvent are emulsified in water. Thereafter, the solvent isremoved to form a latex comprising the block copolymer and the optionaldiluent in water. In some embodiments, the block copolymer is producedin an organic solvent and the solution of block copolymer in organicsolvent produced in the manufacturing process is emulsified in water.Preferably, the polymer concentration in organic solvent is about 8percent by weight or greater and more preferably about 10 percent byweight or greater. Preferably, the polymer concentration in thisembodiment is about 30 percent by weight or less and, more preferably,about 24 percent by weight or less.

In another embodiment, the solution of the block copolymer in organicsolvent can be treated to concentrate the block copolymer to a level ofabout 35 percent by weight or greater and, more preferably, about 40percent by weight or greater. The concentration of block copolymer insolution is about 70 parts by weight or less and, more preferably, about60 parts by weight or less. The block copolymer solution may requireheating to render it processable.

The viscosity of the block copolymer solution must be such that thepolymer solution can be processed. Preferably, the block copolymersolution has a viscosity of about 1,000 centipoise or greater, morepreferably about 10,000 centipoise or greater and, even more preferably,about 25,000 centipoise or greater. Preferably, the block copolymersolution has a viscosity of about 80,000 centipoise or less, morepreferably, about 50,000 centipoise or less and, even more preferably,about 35,000 centipoise or less. One skilled in the art would recognizethat the apparent viscosity of such block copolymer solutions is lowerwhen subjected to high shear conditions and the values above reflect theviscosity under low shear conditions. In the embodiment where the blockcopolymer solution is concentrated, the desired viscosity is achieved byheating the solution to an elevated temperature, preferably, about 25°C. or greater and, more preferably about 45° C. or greater. Preferably,such temperature is about 100° C. or less and, most preferably about 90°C. or less. If the temperature required to achieve the desired viscosityis near or above the boiling point of water or the combined solvent andwater, it is desirable to perform the emulsification under pressure toprevent boiling. The concentrated solution is emulsified in water usinga high shear mixer.

Emulsification of the polymer solution into a water continuous phase maybe accomplished at a wide range of percent polymer solutionconcentrations. The optimum concentration is dependent upon themechanical device used to prepare the emulsion. Thereafter, the blockcopolymer and optional diluent are contacted with water and surfactantwith agitation to emulsify the mixture. After emulsification, thesolvent is removed by conventional means, such as rotary evaporation orvacuum distillation.

In one embodiment the emulsions of block copolymers in water can be usedto prepare films and preferably, the solids level of the organic phasein water is about 20 percent by weight or greater and, more preferably,about 28 percent by weight or greater. Preferably, the solids level isabout 75 percent by weight or less, more preferably, about 65 percent byweight or less.

Generally, the number average size of the resulting polymer particles isless than about 5.0 μm, more preferably from about 0.3 to about 2.0 μmas measured using a Coulter Counter Model Multisizer IIe with a 30 μmaperture tube. Preferably, the polymer particles (the dispersed polymerparticles in the aqueous medium) are spherical in shape.

In another embodiment, the emulsion of the block copolymers can be usedto coat substrates. Such substrates include films, metals, rigidpolymeric articles and the like. Emulsion useful as coatings generallyrequire a lower polymer concentration than those used to prepare films.The concentration should be high enough such that a continuous coatingcan be applied to the substrate, yet not so high as to form a film onthe substrate. Such coatings preferably have a thickness of about 0.05mm or greater and more preferably about 0.1 mm or greater. Preferably,such coatings have a thickness of about 2 mm or less and, morepreferably, about 1 mm or less. Coatings according to this invention canbe applied by conventional means such as by spraying, rolling orpainting the coating on the substrate or alternatively dipping thesubstrate into a bath of the coating.

To prepare a film from the emulsions, a suitable form having a surfacein the shape of the desired resulting product (optionally having asurface coating of a suitable substance to promote film removal and/oremulsion deposition as previously known in the art) is coated with theemulsion and the water is thereafter removed by evaporation. A preferredemulsion for use in the manufacture of dipped goods in the foregoingmanner contains from about 20 to about 70 weight percent of the organicphase, more preferably from about 25 to about 60 weight percent. Asecond or further layer may be applied in the same manner to achievethicker films.

The film resulting from the foregoing procedure may be dried andannealed, if desired, by any suitable technique, especially by heating.Preferable temperatures for drying and annealing are from about 25° C.to about 130° C., more preferably, from about 30° C. to about 120° C.and, most preferably, from about 50° C. to about 100° C. Suitable timesfor drying and annealing are from about 1 minute to about 10 hours,preferably from about 1 minute to about 60 minutes. At highertemperatures, shorter drying and annealing times are required. Thedrying and annealing steps of the process may be conductedsimultaneously or separately. For example, multiple film layers may bedeposited and dried before the resulting structure is annealed.

Alternatively, films may be prepared by casting methods which are wellknown in the art. In brief, a latex of the invention is cast to adesired thickness on a surface from which the film can be subsequentlyremoved. The water is allowed to evaporate. Evaporation can beaccelerated by the use of increased temperature or air flow over thesample. In one embodiment the film is removed from the surface beforeannealing.

The film thickness is determined by the ultimate use. The desired filmthickness for the uses for which the films of the invention may be usedare well known in the art. Preferably, the films have a thickness ofabout 0.10 mm or greater and, more preferably, about 0.20 mm or greater.Preferably, the films are about 3.0 mm or less and, most preferably,about 2 mm or less.

The films of this invention preferably exhibit a tensile strength atbreak of about 11.0 MPa or greater after annealing at 90° C. for about30 minutes. More preferably, the films exhibit a tensile strength ofabout 16.5 MPa or greater and, most preferably, about 21MPa or greaterwhen annealed under such conditions. Tensile strengths are measuredaccording to ASTM-412-87.

Films having adhesive properties may be prepared by incorporating asuitable tackifier, usually a low molecular weight organic polymer suchas a polyterpene or similar compound, in the film. Additional formulantssuch as oils may also be added to modify the adhesive properties of theresulting film. The tackifiers and other formulants may be added to thepolymer solution or incorporated into the emulsion. The resultingmodified emulsion may be further concentrated and coated onto asubstrate such as a masking tape backing. The substrate/film combinationmay thereafter be dried and optionally annealed to form the finalproduct.

Having described the invention, the following examples are provided asfurther illustration and are not to be construed as limiting. Unlessstated to the contrary, parts and percentages are expressed on a weightbasis. Effective phase volumes were calculated using the previouslydisclosed Formulae (II and III). For such calculations, the densities ofthe respective polymer blocks is: polystyrene block 1,047 andethylene-butene block 0.85.

EXAMPLE

The SEBS triblock was prepared by hydrogenating astyrene-butadiene-styrene block copolymer having two styrene chains withan MW of 11,500 Daltons and a central butadiene chain of 56,000 Daltons.The SEBS polymer nominally contained 30 percent oil (Witco 200 oil).

The styrene-co-ethylene-butene-styrene triblock copolymer (SEBS) wasdissolved in cyclohexane to form a 16 percent by weight solids solution.The volume of styrene in the organic phase is 17.2 percent.

This SEBS stock solution was emulsified using a Silverson Model L4R highshear mixer batchwise. A mixture emulsified consisting of 800 grams ofSEBS stock solution (128 grams polymer), 512 grams of water, and 6.8grams of a surfactant, dioctyl sulfosuccinate sodium salt were mixed atmaximum rpm (nominally 5000 rpm) for 5 minutes. During the mixing step,0.3 milliliters of a defoamer was added to prevent excessive foaming.

The solvent removal was accomplished by vacuum devolatilization in arotating glass apparatus with a bath temperature of 90° C. The finishedemulsion, after filtering, was analyzed at 28 percent solids and wasadded to an agitated tank. The agitation was sufficient to mix thesolution but did not introduce any air bubbles into the artificiallatex.

A glass mold at 90° C. with a slightly toughened surface was dipped intoa calcium nitrate and methanol solution (nominally 10 percent solids),removed and allowed to cool to room temperature. The mold was dippedinto the artificial latex with a dwell time of 5 seconds and removed andplaced for a minimum of 5 minutes into a water tank which was maintainedat 40° C. The wet film was dried and annealed in a forced air oven at90° C. for a minimum of 20 minutes and then removed and tested.

The film was free of any holes and possessed a tensile strength ofgreater than 3000 psi (21MPa) tensile. The film was tested for real-timeozone resistance. The ozone resistance test entails die cutting 6 piecesof polymer film from the previously described film. The die used is astandard tensile die of 2 1/2"×1/2" (6.4 cm ×1.34 cm) (ASTM D 1822 TypeL with 1/2" (1.34 cm) tabs). The thin portion of the film was stretchedand secured at either 12.5 percent, 50 percent, or 100 percent of therelaxed length. Two samples at each elongation were prepared. The filmsprepared did not fail after 2400 hours at 12.5, 50 and 100 percentelongations.

What is claimed is:
 1. A process for preparing a film whichcomprises:(1) depositing an aqueous dispersion on a surface underconditions so as to form a film, wherein the dispersion comprises:(a) anorganic phase comprisingone or more block copolymer(s) corresponding tothe formula:

    A-B-X.sub.m -(B-A).sub.n

wherein each A is a polymer block derived from monomers comprising oneor more monovinylidene aromatic monomers and each B is a polymer blockderived from monomers comprising one or more conjugated dishes and,optionally, one or more monovinylidene aromatic monomers, X is theremnant of a multifunctional coupling agent, m is 0 or 1, and n is aninteger from 1 to 5, wherein each A polymer block has a weight averagemolecular weight from 4,000 to 15,000 Daltons, each B polymer block hasa weight average molecular weight from 20,000 to 200,000 Daltons whereinthe block copolymer(s) are hydrogenated such that 99.0 percent orgreater of the residual olefinic unsaturation derived from theconjugated dishes is eliminated and contains sufficient branching suchthat the block copolymer is elastomeric, and(b) a surfactant in asufficient amount to emulsify the organic phase, wherein the effectivephase volume of the A polymer block in the organic phase is from about 8to about 20 volume percent; (2) removing the film from the surface; and(3) annealing the film under conditions such that the film exhibits atensile strength at break of 11,0 MPa or greater after annealing.
 2. Aprocess according to claim 1 wherein the film is annealed at 30° C. to120° C. for 1 to 60 minutes.
 3. A coherent, elastomeric, solid,free-standing film comprising an organic phase comprising one or moreblock copolymer(s) corresponding to the formula:

    A-B-X.sub.m -(B-A).sub.n

wherein each A is a polymer block derived from monomers comprising oneor more monovinylidene aromatic monomers, each B is a polymer blockderived from monomers comprising one or more conjugated dienes and,optionally, one or more monovinylidene aromatic monomers, X is theremnant of a multifunctional coupling agent, m is 0 or 1, and n is aninteger from 1 to 5, each A polymer block has a weight average molecularweight from 4,000 to 15,000 Daltons, each B polymer block has a weightaverage molecular weight from 20,000 to 200,000 Daltons, wherein theblock copolymers are hydrogenated such that about 99 percent or greaterof the residual olefinic unsaturation derived from the conjugated dienesis eliminated and contains sufficient branching such that the blockcopolymer is elastomeric, wherein the effective phase volume of the Apolymer block in the organic phase is from about 8 to about 20 percent,wherein the film is prepared from an aqueous dispersion, annealed anddemonstrates a tensile strength of 11.0 MPa or greater.
 4. A filmaccording to claim 3 which demonstrates a tensile strength of 16.5 MPaor greater.
 5. A film according to claim 4 which further comprisesanextender comprising a naphthenic or aliphatic hydrocarbon oil or apolymer compatible with the 3 block of the copolymer.
 6. A filmaccording to claim 4 which comprises two or more block copolymerswherein each A polymer block has a weight average molecular weight offrom about 4,000 to about 15,000 Daltons.
 7. A film according to claim 4wherein the block copolymer is derived from styrene and 1,3-butadiene orisoprene.
 8. A film according to claim 7 wherein the effective phasevolume of the A polymer blocks in the organic phase is from about 10 toabout 18 volume percent.
 9. A film according to claim 8 wherein theweight average molecular weight of the one or more block copolymers isfrom about 50,000 to about 300,000 Daltons.
 10. A film according toclaim 6 wherein each A polymer block of the two or more block copolymershas a weight average molecular weight of from about 6,500 to about15,000 Daltons.
 11. A film according to claim 10 wherein the A polymerblock is derived from styrene and the B polymer block is derived from1,3-butadiene or isoprene.
 12. A film according to claim 10 wherein theeffective phase volume of the A polymer block in the organic phase isfrom about 10 to about 18 percent.
 13. A film according to claim 12wherein the weight average molecular weight of the block copolymers isfrom about 50,000 to about 300,000 Daltons.
 14. A process according toclaim 2 wherein the organic phase further comprises an extendercomprising a naphthenic oil, aliphatic hydrocarbon oil or a polymercompatible with the B block of the copolymer.
 15. A process according toclaim 14 wherein the surfactant is present in an amount of from 0.5 to10 percent by weight.
 16. A process according to claim 15 wherein theblock copolymer is derived from styrene and 1,3-butadiene or isoprene.17. A process according to claim 16 wherein the effective phase volumeof the A polymer block in the organic phase is from about 10 to about 18volume percent.
 18. A process according to claim 2 which comprises twoor more block copolymers and a surfactant wherein each A polymer blockof the two or more block copolymers has a weight average molecularweight of from about 6,500 to about 15,000 Daltons.
 19. A processaccording to claim 18 wherein the surfactant is present in an amount offrom about 0.5 to about 10 percent by weight.
 20. A process according toclaim 19 wherein the A polymer block is derived from styrene and the Bpolymer block is derived from 1,3-butadiene or isoprene.